The present invention relates generally to steam generators and, more particularly, to the manufacture of steam generators in which a sandwich nipple plate is incorporated to provide a uniform flow of steam to a moisture separating apparatus.
In applications where it is desirable to reduce moisture content of steam, one method for performing this function is to direct a flow of steam between a plurality of chevron plates which are arranged in such a way that the moisture-laden steam is impacted against a plurality of discontinuities in the chevron plates. As the steam impacts these discontinuities, some of its entrained moisture is deposited on the chevron plates and thus removed from the steam. This deposited moisture is then conducted away from the steam path towards a drain system.
In order to improve the moisture separating efficiency of this type of moisture separator, it has been found that the provision of a perforated plate upstream from the chevron plates is advantageous. The function of the perforated plate is to distribute the steam in a uniform flow pattern prior to its passage between the chevron plates. A typical application of a moisture separator of this type is a steam generator of a nuclear power plant system.
These perforated plates also beneficially cause a portion of the moisture to be separated from the steam as the moisture laden steam impacts the portions of the plate which are not perforated. However, this additional beneficial moisture removing characteristic of the perforated plates can be diminished if the separated moisture is subsequently drawn through the perforations as it runs down along the impaction surface of the perforated plate. In order to take full advantage of the moisture separating characteristics of the perforated plate, it has been found that the addition of tubes, or nipples, can prevent the separated moisture from being drawn through the perforations by the normal flow of steam passing through a plurality of holes in the perforated plate.
These tubes, or nipples, are disposed in a way so that they extend through holes in the perforated plate in a direction away from the chevron plates and toward the incoming flow of steam. Therefore, as the moisture which has been separated from the steam by the perforated plate passes in a downward direction along the impaction surface of the perforated plate, the nipples prevent the steam from carrying this moisture through the perforated plate in a direction toward the chevron plates.
The tubes, or nipples, can be attached to the perforated plates in a number of ways. For example, the fastening of the nipples to the plate can be accomplished by welding, rolling or hydraulic expansion. However, a plurality of perforated plates is used in a steam generator and each of these perforated plates would require multiplicity of nipples attached to it. Since a typical steam generator would typically necessitate the use of over 13,000 nipples, a four-loop nuclear plant would require over 24,000 nipples even if only the lower dryer here was designed in this way.
Obviously, if conventional manufacturing methods were used to attach the nipples to the perforated plates, their manufacture would become so costly that serious consideration of their use would be essentially eliminated. In order for perforated plates of a steam generator to be equipped with nipples so that moisture which is collected on the plate can be prevented from being swept into the chevron plate of the dryer, some practical means for manufacturing the improved nippled plates is necessary.
The present invention provides a means for manufacturing nippled plates for steam generators which does not necessitate the welding, rolling or hydraulic expanding of each of the nipples. In a steam generator made in accordance with the present invention, two perforated plates are used in conjunction with a plurality of tubes which each have one of their ends upset. A first of the two plates is provided with a plurality of holes which are shaped to receive the tubes in sliding relation therein. The holes of this first plate are shaped so that the tubes can easily be inserted into them. These holes of the first plate are also sized in such a way that the upset portion of each of the tubes cannot pass through them.
After inserting a plurality of the tubes through the holes of the first plate, a second plate is disposed against the first plate in such a way that it prevents the passage of the tubes out of the first plate in a reverse direction from the initial assembly procedure described above. After assembly, the first and second plates are associated proximate each other with their planar surfaces parallel. The plurality of tubes are disposed in such a way that they extend through the first plate and away from both plates. Following an assembly procedure of the type described above, the two plates are fastened together by either welding or bolting.
The present invention does not require the welding, rolling or hydraulic expanding of the individual tubes and therefore significantly reduces the labor intensive operations required to manufacture a nippled perforated plate and the overall cost thereof.